Clinical
Dental Tribune | March, 2009
Minimally invasive and biomimetic endodontics: The final evolution? David J. Clark, DDS
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raditional endodontics has been based on feel, not sight. Tactile proprioreception was the only guide as burs and files were blindly inserted into pulp chambers and root canal systems. Together with radiographs and electronic apex locators, this blind approach has produced surprising success that, in
the words of Dr. Eric Herbransen, “the endodontics succeeds often in spite of us.” There is, however, a significant failure rate, especially long-term failure, that is driving mainstream dentistry to aggressively extract natural teeth in favor of implants. The sting of clinical failure is a powerful motivator for change. In this article, I will describe the rationale and techniques involved in minimally traumatic endodontic access and shaping (Part I). In my upcoming Webinar I will discuss obturation techniques for smaller and non-round endodontic shapes, which will also appear as a follow up article in this publication (Part II).
Ribbons, sheets & banners
Fig. 1: An immature maxillary molar is sectioned and viewed from the apical aspect.
Fig 2: This lower bicuspid was treated with a generous crown-down endodontic shape and suffered a retrograde root fracture within three years of the endodontic treatment.
Figure 3: This radiograph demonstrates a thirtyone year success with delicate shaping and crude obturation with silver points (#14), and a four-year failure with a large crown-down shape and heated gutta-percha (note the lesion on #13).
One of the most distressing “hangovers” of the era of blind endodontics and endo-restorative is the belief that canal systems are straight, exit at the radiographic apex and are round in cross section. In reality, most canal systems curve and exit short of the radiographic terminus. A very large number, at least 50 percent, are ovoid or super-ovoid in cross section. Figure 1 demonstrates that of the three roots and canal systems shown, only one is round. As these canal systems mature, they narrow into a variety of unpredictable ovoid shapes often with smaller anastamosing canal systems (Figs. 4–6).
The evolution of endodontic shaping
The original endodontic shape was established based on mostly hand filing and filled with either silver points or cold lateral condensation of guttapercha. Sargenti later introduced a more rapid approach that involved machine-driven instruments (rotary files) creating larger shapes with significantly more dentin removal. As of late, a “crown down” approach is now popular. The roots are rapidly and blindly machined. This can result in better obturation of the apical half because of improved penetration of irrigation during instrumentation and improved hydraulics during obturation. But at what cost (Fig. 2)?
Is crown down endo actually better than lateral condensation?
Fig. 4: This mandibular incisor appears so frail with a lingual view or radiographic image. It appears husky with a mesial view. It is at least twice as broad buccal lingually.
The outcome studies are inclusive, but what we do know is that the success rate today is no better than it was 40 years ago (Fig. 3). The advantages of crown down are often offset by the weakening caused by Gates-Glidden burs and orifice shapers. The short-term thrill of the radiographic “puff of sealer” at the apex is lost when the tooth implodes a few years down the line. Residual dentin is directly related to longterm strength and has indisputably been shown as the key to long-term
tooth retention. In contrast, the supposed strengthening of the root from a “monoblock” of bonded resin obturation, bonded core and fiber post is proving to be inconsistent.1 Another startling revelation is that the dentin in an endodontically treated tooth is not more brittle than in a vital tooth.2–4 In short, preservation of peri-cervical dentin and ferrule girth trump all other factors.
Ovoid canal systems & roots are non-round for a reason Rotary instruments and obturating points of gutta-percha are round because of the limitations of their mechanical nature. They create anatomically appropriate shapes in round roots, but fail in ovoid roots. Over the ages, the dynamics of occlusion and arch form have guided the development of human tooth roots such that at least half have ovoid roots.
Smaller and/or ovoid shaping: Why and how? Why Biomimetics is a treatment approach that has, as its ultimate
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goal, to retain as much of the natural tissue as practical, and to mimic the physics and structures of the human body. There is nothing biomimetic about a stiff, round rod (prefabricated post) running through the center of an ovoid root. The natural ovoid root is essentially a semi-rigid pipe deriving its strength from without, not within. The endodontic and endo-restorative goal should be to mimic the pulp space that was present when the tooth was young. From that point, it can be argued that any secondary dentin that is deposited adds little additional strength because of the amorphous and irregular deposition pattern. This point is supported by the robust strength of young teeth with large pulp chambers and large radicular pulp spaces. If a small round access that does not disturb primary dentin can allow instruments to engage potentially significant complex anatomy (e.g., a second or third major system and corresponding portals of exit), then the round access is acceptable. The reality of ovoid roots would seem to disagree with this approach. Creating a large round access that results in removal of primary dentin of the delicate, narrow portion of the root is the common approach today. While this can allow access to complex branching of systems that AD